Spinning self-crimping composite fibers

ABSTRACT

SELF-CRIMPING COMPOSITE FIBERS OF ACRYLONITRILE POLYMER COMPONENTS, ALL OF THE SAME ACRYLONITRILE POLYMER BUT SOME OF WHICH CONTAIN FINELY DISPERSED SILICA PARTICLES TO REDUCE SHRINKAGE THEREOF AND THE REST OF WHICH CONTAIN WATER-INSOLUBLE PLASTICIZER, E.G., ORGANIC PHOSPHATE OR PHOSPHITE TO INCREASE SHRINKAGE THEREOF AN EXPOSURE TO HEAT SO CRIMP IS DEVELOPABLE AT ELEVATED TEMPERATURE. SUCH FIBERS ARE MADE BY PREPARING A PLURALITY OF POLYMER SOLUTIONS OF THE SAME POLYMER AND THE SAME POLYMER CONCENTRATION, DISPERSING FINELY DIVIDED SILICA PARTICLES IN SOME BUT NOT ALL THESE POLYMER SOLUTIONS, DISPERSING A WATER-INSOLUBLE LIQUID PLASTICIZER IN THE REST OF THE POLYMER SOLUTIONS, AND SPINNING SUCH SPINNING SOLUTIONS TO FORM COMPOSITE FIBERS BY A PROCESS WHICH INCLUDES THE STEPS OF STRETCHING THE FIBERS AND SUBSEQUENTLY RELAXING THE FIBERS AT ELEVATED TEMPERATURE IN A FREE-TO-SHRINK CONDITION TO DEVELOP CRIMPINESS THEREIN.

3,798,296 SPINNING SELF-CRIMPING COMPOSITE FIBERS James Kellett Thomas,Pensacola, Fla., assignor to American Cyanamid Company, Stamford, Conn.No Drawing. Filed July 28, 1972, Ser. No. 276,192 Int. Cl. B29f 3/10 US.Cl. 264-171 6 Claims ABSTRACT OF THE DISCLOSURE Self-crimping compositefibers of acrylonitrile polymer components, all of the sameaerylonitrile polymer but some of which contain finely dispersed silicaparticles to reduce shrinkage thereof and the rest of which containwater-insoluble plasticizer, e.g., organic phosphate or phosphite toincrease shrinkage thereof on exposure to heat so crimp is developableat elevated temperature. Such fibers are made by preparing a pluralityof polymer solutions of the same polymer and the same polymerconcentration, dispersing finely divided silica particles in some butnot all these polymer solutions, dispersing a water-insoluble liquidplasticizer in the rest of the polymer solutions, and spinning suchspinning solutions to form composite fibers by a process which includesthe steps of stretching the fibers and subsequently relaxing the fibersat elevated temperature in a free-to-shrink condition to developcrimpiness therein.

This invention relates to novel self-crimping synthetic fibers ofacrylonitrile polymer and to a method for producing them.

It is well known and in widespread commercial practice to manufacturefibers from acrylonitrile polymers by various spinning processes. Whilethese various processes have numerous differences, they all have certainfeatures in common. In all these processes, the acryloni' trile polymeris dissolved in a solvent to form a spin dope which is extruded throughspinnerette orifices to form an extrudate which is then coagulated orsolidified to form fibers. In these processes, the fibers are stretchedto orient the molecules therein and thereafter relaxed to ease molecularstrains accompanied by shrinkage of the fibers. Depending on theparticular process being employed, additional steps may be involved,such as incorporating additives in the spin dope, washing the fibers,drying the fibers, restretching the relaxed fibers, applying finishes,cutting to form staple fibers, etc.

The products resulting from these processes as described above aresubstantially straight fibers. Natural fibers, such as wool and cotton,have many desirable properties due to their crimpiness. It was earlyrecognized that these fibers of acrylonitrile polymer would be bettersuited for many uses if they were made crimpy.

One general approach which has long been in commercial use is tomechanically crimp these fibers of acrylonitrile polymer. Severalspecific techniques have evolved. In gear crimping, the fibers arepassed through the nip of a pair of coacting gears. In stuffer crimping,the fibers are compacted or stuffed into a confined zone or stuffing boxunder pressure. In twist crimping, the fibers are tightly twisted andthen untwisted. In all of these processes, crimp is imparted to thefibers by the application of mechanical forces to the fibers, usually atelevated temperature. Because of well-recognized deficiencies of theproducts of these processes, such as physical damage to the fiberscaused by the crimping apparatus and loss of crimpiness during textileprocessing due to stresses and heat, a second general approach has foundcommercial favor in recent years.

A second general approach which was first invented about 1942 and whichhas found significant commercial "United States Patent 3,798,296Patented Mar. 19, 1974 use since about 1960 is to produce compositefibers whose components shrink by different amounts when exposed toidentical conditions. In this process, two or more distinct spinningsolutions are simultaneously extruded through each orifice of aspinnerette to form a composite extrudate which is then coagulated orsolidified to form composite fibers. Thereafter, these composite fibersare processed by steps which include, in the case of composite fibers ofacrylonitrile polymer, stretching to orient the molecules therein andthereafter relaxing to ease molecular strains accompanied by shrinkageand crimping of the fibers. Depending on the particular process beingemployed, additional steps may be involved, such as those mentionedabove for producing regular acrylonitrile polymer fibers.

Several types of composite fibers, differing in the physical dispositionof the components thereof, are known. In side-by-side composite fibers,the components are disposed alongside each other along the length of thefiber, as illustrated and described in Kulp et al. US. Pat. 2,386,173;Sisson et al. US. Pat. 2,428,046; Ryan et al. US. Pat. 2,988,420; andFujita et al. US. Pat. 3,182,106. In sheath-core composite fibers, thecomponents are disposed one within and completely surrounded by anotherthroughout the fiber length, as illustrated' and described in Breen US.Pat. 2,987,797; Breen US. Pat. 3,038,236, FIGS. 8, 12, and 13; Fukuma etal. US. Pat. 3,500,498; and Ueda et al. US. Pat. 3,541,198. In randomcomposite fibers, the components are randomly disposed within andadjacent each other, as illustrated and described in Miller US. Pat.2,805,465; Baer US. Pat. 3,182,352; Powell et al. US. Pat. 3,295,552;and Matsui et al. US. Pat. 3,613,173. In each of these compositeconfigurations, one component shrinks more than another during sometreatment, usually by heat in an unrestrained state, to develop coilycrimp. The present invention relates to an improvement in thistechnology of producing composite fibers of acrylonitrile polymers andis particularly related to producing the difference in shrinkagebehavior needed for crimp formation.

In the production of composite fibers, it is important that thecomponents adhere to each other and not split apart during the expectedlife of the products made therefrom, which requires that the componentsbe compatible.

It is also important that all the components be spinnable using somecommon spinning conditions since they must all be spun simultaneouslythrough each spinnerette orifice. It is also important, as noted above,that the components shrink by difierent amounts when subjected to sometreatment, such as exposure to heat in a relaxed, free-to-shrinkcondition. Commercially, this treatment is preferably exposure to steam,hot water, or heated air since the materials used are inexpensive,non-polluting, and easily removed from the fibers.

The most widely used technique is to select similar polymers ofdifiering chemical composition for each component, as exemplified inFujita et al. US. Pat. 3,182,106 where the polymers comprise the samemonomers but in different proportions, or Calhoun US. Pat. 3,006,028where the components were a homopolymer and a copolymer ofacrylonitrile. Each polymer must be separately made and separatelydissolved to form separate spinning solutions which necessarily involvesduplication of facilities and increased costs. In order to avoid some ofthese disadvantages (viz, those associated with requiring a plurality ofdifferent polymers), it has been proposed to use one polymer but toprepare a plurality of spinning solutions of different concentrationstherefrom, as in Dawson et al. US. Pat. 3,084,993. The amount ofdifferential shrinkage obtainable by this method is very small and onlya limited amount of crimpiness is obtainable. This 3 process, moreover,still requires the duplication of dissolving and solution handling withthe attendant increased costs. The present invention relates toimproving this technology still further so as to achieve highdifferences in shrinkage while using only a single polymer and only asingle spinning solution to substantially eliminate the necessity forduplication of facilities and reduce costs.

In accordance with the present invention, composite fibers ofacrylonitrile polymer are prepared wherein each component thereof is theidentical polymer and wherein the necessary shrinkage difference resultsfrom the inclusion of finely dispersed silica in at least one but lessthan all the components and the inclusion of a waterinsoluble liquidplasticizer for acrylonitrile polymers in the rest of the components.Preferably, this is accomplished by preparing one acrylonitrile polymerand dissolving it in a solvent to form a spinning solution. Just priorto extrusion, this solution is subdivided into a plurality of streamsand finely divided silica is mixed into one or more streams, but notinto all streams, and the water-insoluble liquid plasticizer is mixedinto the remaining streams, and the separate streams are spun togetherusing any of the apparatus for spinning composite fibers, such as thosedepicted in the various patents cited above. The methods chosen formixing the silica and the waterinsoluble liquid plasticizer are notcritical as long as the silica and the plasticizer are finely dispersedin the respective acrylonitrile polymer solutions.

The acrylonitrile polymers useful for the practice of this inventionshould contain at least about 70% polymerized acrylonitrile and up to30% ethylenically unsaturated comonomers polymerizable therewith.Numerous such comonomers are known, such as those disclosed in U.S.Pats. 2,874,446; 2,948,581; 3,222,118; and the various other patentsreferred to therein. Any of the usual solvents for acrylonitrilepolymers can be used to prepare solutions thereof, such as the organicsolvents, e.g. dimethylformamide, dimethylacetamide, ethylene carbonate,and aqueous salt solvents, e.g. those disclosed in U.S. Pats. 2,140,-921; 2,558,730; and 2,648,647 although other solvents may be usedprovided they are inert to the silica and the water-insoluble liquidplasticizer to be dispersed therein. The spinning solutions can be spuninto fibers using the wet, dry, and air-gap spinning procedures wellknown in the art. It is only necessary that such procedure include astretching step to orient the acrylonitrile polymer molecules in thefibers and thereafter a relaxating step to ease the molecular strains topermit shrinkage and crimp development, as is usual in processes formaking composite fibers of acrylonitrile polymers.

The silica particles useful for the practice of the present inventionare commercially available products which characteristically are ofextremely small particle size, e.g., less than about 300 angstrom units;have a large surface area, e.g., greater than about 100 square metersper gram; and contain surface reactive hydroxyl groups. Among suchsilica products are the fumed silicas, such as Aerosil sold by DegussaInc. and Cab-O-Sil sold by Cabot Corp., and the colloidal silicas, suchas Ludox sold by Du Pont, Nalcoag sold by Nalco Chemical Co., and Nyacolsold by Nyacol Inc. Further descriptions of some of these silicas can befound in Pruett U.S. Pat. 3,156,666 and Precopio et a1. U.S. Pat.2,888,424 and the various technical bulletins of the aforesaid vendorsof these products. In such bulletins, Aerosil fumed silica is describedas produced by flame hydrolysis of silicon tetrachloride in the gasphase at 1100 C. and Ludox colloidal silica is described as produced bythe teachings of Bechtold et al. U.S. Pat. 2,574,902 and Rule U.S. Pat.2,577,485. These silica products are widely known, having found numerousapplications in diverse industries. I

Any water-insoluble liquid plasticizer for acrylonitrile polymers may beused for the practice of the present invention. Especially preferred arethe water-insoluble liquid organic phosphates and phosphites having theformulae:

wherein R R and R are each selected from alkyl of 3 to 18 carbon atoms,alkoxyalkyl of 4 to 18 carbon atoms, phenyl, and lower-alkyl-substitutedphenyl, which may contain chlorine and/or bromine substituents thereon.Illustrative of such compounds are tridecyl phosphate,dipropyl-octadecyl phosphite, tricresyl phosphate, tr1- benzylphosphate, isooctyl-diphenyl phosphite, tris[2,2bis(propoxymethyl)butyl] phosphate, tris(2,3-dibromopropyl) phosphate,tri[2 bromo 1 (chloromethyDethyl] phosphate,tris(2,3-dichloropropyl)phosphate, tris[2- chloro-l-(chloromethyl)ethyl]phosphite, 2,4,6-tribromophenyl bis(isopropyl) phosphate,tris[2,2-bis(2,3 dibromopropoxymethyl)butyl] phosphate,dicyclohexyl-isopropyl phosphite, etc.

As pointed out above, it is known to prepare composite fibers ofacrylonitrile polymer by spinning processes which include the steps ofstretching the composite fibers to orient the molecules therein andrelaxing the previously stretched composite fibers to ease molecularstrains accompanied by shrinkage and crimping of the fibers due to thedifference in amounts of shrinkage among the components thereof. In suchprocess, the present invention relies on the addition of silicaparticles to at least one but less than all the components of thecomposite fiber and of the water-insoluble liquid plasticizer to theremaining components to produce the shrinkage dilferential needed forcrimp development during the relaxing step. Thus, the composite fibersof the present invention preferably have all components of the sameacrylonitrile polymer and they are spun from acrylonitrile polymersolutions which preferably are of the same polymer concentration in thesame solvent, i.e., they are identical polymer solutions differingsolely in the presence of silica particles and water-insoluble liquidplasticizer separately in the various components for crimp formation.However, other additives, such as dyes, etc. may be present providedthey do not affect the shrinkage characteristics of the fiber.

It is not known why the inclusion of silica particles into theacrylonitrile polymer matrix reduces the ability of the polymercomponent to shrink on exposure to elevated temperature, although it isbelieved that such particles produce a rigidity effect restrictingmovement of the polymer molecules. It is also not known why theinclusion of the plasticizer into the acrylonitrile polymer matrixincreases the ability of the polymer component to shrink on exposure toelevated temperature, although it is believed that such liquidplasticizer enables the polymer molecules to slide past each other moreeasily by reducing intermolecular friction. In any case, theacrylonitrile polymer components containing such silica particles shrinkless and the acrylonitrile polymer components containing such liquidplasticizer shrink more than corresponding acrylonitrile polymercomponents devoid of such additives at conditions causing shrinkage.

In the composite fibers of this invention, sufficient differentialshrinkage to cause self-crimping during relaxation is achieved whenabout 2.0 to 10.0%, preferably 3.0 to 8.0, of silica particles on weightof polymer is dispersed in one component of the composite fibers and 3to 30%, preferably 5 to 25% of the liquid plasticizer is dispersed inanother component of the composite fibers. The exact amounts are notcritical, but depend on the amount of crimpiness desired, thedistribution and relative proportions of the polymer components, and therelaxation or shrinkage conditions. In general, it appears that there isabout a one percent reduction in shrinkage for every one percent ofsilica included in the acrylonitrile polymer component containing silicaand about a one percent increase in shrinkage for every one percent ofliquid plasticizer included in the acrylonitrile polymer componentcontaining plasticizer. Quantities in excess of about silica arenormally to be avoided due to excessive thickening of the spinningsolution causing problems in extruding such viscous solutions.

This invention will now be illustrated by the following examplesdepicting preferred embodiments thereof, it being understood that theinvention is not limited to such embodiments.

EXAMPLE 1 A large quantity of a spinning solution containing 9.9 percentof a copolymer of 81% acrylonitrile, 10% vinylidene chloride, and 9%methyl methacrylate, 46.0 percent sodium thiocyanate, and 44.1 percentwater was prepared and divided into a plurality of portions. A silicamasterbatch containing 10.53 percent silica, 42.00 percent sodiumthiocyanate, and 47.47 percent water was also prepared.

Portion 1 of this spinning solution was split and flowed through twoparallel flow paths, path A receiving about 60% and path B receivingabout 40%. Into the spinning solution flowing in path A was continuouslymixed at sufficient qu ntity of tris (2,3-dibromopropyl) phosphate toresult in the spinning composition A containing 0.95%tris(2,3-dibromopropyl)phosphate well dispersed therein. Into thespinning solution flowing in path B was continuously mixed 2. sufficientquantity of the silica masterbatch to result in spinning composition Bcontaining 0.51% silica well dispersed therein. These two spinningcompositions A and B were then flowed through a static mixer to provideslight random mixing of the two spinning compositions. The two randomlymixed spinning compositions were then extruded together through aspinnerette into a cold (about 3 C.) dilute (13.5% salt concentration)aqueous sodium thiocyanate coagulant to form wet gel filaments whichwere, in sequence, stretched in air at room temperature to 2.5 timestheir unstretched length, washed wih water to remove residual sodiumthiocyanate, stretched another 4 times (to a total of 10 times the unstretched length) in water at 99 C., and dried in a relaxed condition ina humid atmosphere at 127 C. dry bulb and 6 and about 2.7% silica ontotal weight of fiber). After processing this staple fiber into yarn (2ply s Philadelphia count) on conventional textile equipment andimmersing the yarn in boiling water, the crimpiness was redeveloped, andthe yarn had a specific bulk of 7.7 cubic centimeters per gram.

In a control run in which all conditions were the same as above exceptthe tris(2,3-dibromopropyl) phosphate and silica were omitted, no crimpdeveloped during the steam relaxation step and the yarn, after immersionin boiling water, had a specific bulk of only 3.5 cubic centimeters pergram.

EXAMPLES 2-4 Portions 2, 3, and 4 were each split into two parts, eachpart admixed with tris(2,3-dibromopropyl) phosphate or silicamasterbatch, the two parts were slightly random mixed in a static mixer,spun into fibers, and converted to yarn using the same process as inExample 1 except that the concentrations of tris(2,3-di'bromopropyl)phosphate and silica added were varied.

For instance, in Example 2, sufficient tris(2,3-dibromopropyl) phosphatewas admixed into the split in path A to result in the spinningcomposition A containing 1.48% tris(2,3-dibromopropyl) phosphate welldispersed therein and sufiicient silica masterbatch was admixed into the40% split in path B to result in the spinning composition B containing0.92% silica well dispersed therein. After spinning, etc., as in Example1, analysis of the staple fibers indicated that the A componentcontained about 13.2% tris(2,3-dibromopropyl) phosphate and the Bcomponent contained about 9.7% silica (for an overall analysis of about7.9% phosphate and about 3.9% silica on total weight of fiber). Totalshrinkage due to the drying and steam-relaxing steps was 39% of thestretched length and considerable crimpiness developed. After immersingthe yarn made from the straightened and mechanically crimped fibers inboiling water, the crimpiness redeveloped and the yarn had a specificbulk of 8.9 cubic centimeters per gram.

In a similar manner, in Examples 3 and 4, other concentrations of thesesame additives were utilized to produce fibers. The results of thesetests, along with the results of the tests of Examples 1, 2, and thecontrol run 69 C. wet bulb for 15 minutes (as taught by Robertson 45(without additives), are reported in the following table.

TABLE Analysis of fibers, percent Phosphate, Silica 1n Phos- PercentYarn Compocompo phate in Silica in total bulk Example nent A nent Bfiber fiber shrinkage emi /gm.

Control 0 0 0 0 40 8.5 10.3 6.7 6.2 2.7 43.5 7.7 13.2 9.7 7.9 3.9 39.08.9 24.7 7.2 14.8 2.9 45.2 10.3 25.8 6.0 15.5 2.4 43.3 9.3

et al. US. Pat. 2,984,912) to collapse the fiber structure. During thisdrying step, the fibers shrank about 20% of their stretched length, anamount not sufficient to cause crimp development. The dried filamentswere then exposed to steam at 125 C. for 60 seconds in a relaxedfree-toshrink condition, during which the filaments shrank additionallyto a total shrinkage of 43.5% of their stretched length and considerablecrimpiness developed. The filaments were then restretched slightly(enough to straighten out the crimpiness) in Water at 88 C. and thenquenched in water at 70 C. while under tension to yield straightenedfilaments. These straightened filaments were then mechanically crimpedat 80 C. to give two to six crimps per inch, dried at C., and cut intostaple fibers averaging 16.65 denier. Analysis of these fibers indicatedthat the A component contained about 10.3% tris(2,3-dibromopropyl)phosphate and the B component contained about 6.7% silica (for anoverall analysis of about 6.2% phosphate In a similar manner, crimpycomposite fibers of acrylonitrile polymer can be prepared usingspinnerette assemblies which produce side-by-side or sheath-corecomposite fibers. Also, other water-insoluble liquid plasticizers can beused in lieu of the specific phosphate illustrated in the foregoingexamples without departing from the teachings of this invention.

I claim:

1. In the process of spinning composite fibers of acrylonitrile polymerby simultaneously extruding through each orifice of a spinnerette aplurality of acrylonitrile polymer solutions, which process includes thesteps of stretching the fibers and subsequently relaxing the fibers atelevated temperature in a free-to-shrink condition, the improvementcomprising preparing a plurality of acrylonitrile polymer spinningsolutions of the same polymer and the same polymer concentration anddispersing (a) finely divided silica particles in at least one but lessthan all said polymer solutions and (b) a waterinsoluble liquidplasticizer for acrylonitrile polymers in the rest of said polymersolutions prior to extrusion, said fibers developing crimp during saidrelaxing step due to the presence of the finely divided silica and theplasticizer in separate polymer components of the resulting compositefiber.

2. A process as defined in claim 1 wherein said relaxing is by exposureto steam.

3. A process as defined in claim 1 wherein said silica has a particlesize of less than about 300 angstrom units, a surface area greater thanabout 100 square meters per gram, and surface reactive hydroxyl groups.

4. A process as defined in claim 1 wherein 2.0 to 10.0% on weight ofpolymer of silica is dispersed in each acrylonitrile polymer solutioncontaining same.

5. A process as defined in claim 1 wherein said waterinsoluble liquidplasticizer is a water-insoluble liquid organic phosphate or phosphitehaving the formula:

wherein R R and R are each selected from the group of moietiesconsisting of alkyl of 3 to 18 carbon atoms,

alkoxyalkyl of 4 to 18 carbon atoms, phenyl, and loweralkyl-substitutedphenyl, and such moieties containing chlorine or bromine substituentsthereon.

6. A process as defined in claim 1 wherein 3 to on weight of polymer ofplasticizer is dispersed in each acrylonitrile polymer solutioncontaining same.

References Cited UNITED STATES PATENTS JAY H. WOO, Primary Examiner US.Cl. X.R.

26029.6 AN, 29.6 AG, 29.6 MP, 30.6 R, 41 R, 41 C; 264168, 182, 211

